64 THE CHROMOSOMES 



has only just divided in prometaphase and whose 

 component halves are still in contact). As a result 

 all the spindle attachments lie in the equatorial 

 plane. At meiosis, on the other hand, each bivalent 

 possesses two spindle attachments, one belonging to 

 the maternal chromosome, the other to the paternal 

 one. These are in general fairly far apart and they 

 arrange themselves at equal distances above and 

 below the equatorial plane, i.e. between this and the 

 poles of the spindle. The spindle attachments have not 

 divided y nor do they do so until the second meiotic 

 division. 



Anaphase of FmsT Meiotic Division 



At the anaphase of the first division the whole 

 spindle attachments play the same role as the split 

 halves of the spindle attachments play at an ordinary 

 mitotic anaphase. As they separate (repelling one 

 another exactly as the split halves do at mitosis) they 

 drag after them the chromatids which are attached 

 to them. As they do so the chiasmata which have 

 not already been ' terminalized ' move along to the 

 ends of the bivalent away from the spindle attach- 

 ment and slip off at the end. Chromosomes which 

 are only associated by means of ' terminal chiasmata * 

 are simply torn apart as the spindle attachments 

 repel one another. Each spindle attachment as it 

 moves towards the pole drags after it (either on the 

 surface of the spindle or in its substance) two chrom- 

 atids. If the spindle attachment is median or sub- 

 median these will form a structure with four arms 

 of more or less equal length with the spindle attach- 

 ment at their point of junction (as in the case of the 

 larger chromosome in Fig. lOh and chromosome A in 

 Fig. 16a). If, on the other hand, the spindle attach- 

 ment is sub -terminal, two of the arms will be very 

 short and the general appearance of the chromosome 

 will be that of a V (smaller chromosome in Fig. lOh 

 and chromosomes B and C in Fig. 16a). 



